Investigating the relationships of structural and functional neural networks of primary visual cortex with engineered AAVs and chemogenetic-fMRI techniques

Rationale: Neural networks are crucial for brain function, but the relationship between functional and structural networks remains unclear, hindering disease understanding and treatment. This study employs AAVs, MRI reporter gene (AQP1), and chemogenetic-fMRI to explore the relationship between structural and functional connectivity in the mouse primary visual cortex (V1), offering a novel approach to study abnormal brain functions. Methods: The rAAV-PHP.eB-DIO vector encoding AQP1 was used to cross the blood-brain barrier and infect the brain, enabling in vivo diffusion-weighted imaging (DWI-MRI) to assess the anterograde structural connectivity network of V1. Additionally, chemogenetic activation of V1 using a Cre-dependent system was performed, and the whole-brain BOLD responses were evaluated using fMRI. The integration of these techniques provided a comprehensive analysis of the relationship between functional and structural connectivity. Results: This study successfully achieved the combined detection of structural and functional connectivity in the V1 of mice. The rAAV1-hSyn-Cre virus was utilized for monosynaptic anterograde tracing. Additionally, a blood-brain barrier-crossing serotype viral vector, rAAV-PHP.eB-DIO-AQP1-EGFP, was intravenously injected to effectively transduce AQP1 into the V1 region and its downstream areas. The results indicated that regions expressing AQP1 under the control of Cre recombinase, including V1, LGN, CPu, and SC, exhibited significant alterations in DWI signal intensity (SI) and apparent diffusion coefficient (ADC). DREADD-fMRI analysis revealed that chemogenetic activation of the V1 region significantly enhanced neural activity in related brain regions, accompanied by a notable increase in BOLD signals. These regions included CPu, HIP, TH, SC, and PAG. Conclusion: In vivo decoding of neuronal activity and structural connectivity provides insights into brain structure-function interplay, which was important for understanding the cerebral function.